The present invention relates to a document scan apparatus provided with an auto document feeder.
Various document scan apparatuses which scan documents in a document scan portion have been conventionally provided. There are generally two methods for scanning documents in the document scan portion. In one method, the documents are fixed and scanned by moving an optical system. In the other method, so called flow scanning, documents are moved and scanned by a fixed optical system.
Further, document scan apparatuses having an auto document feeder (ADF) have been conventionally provided. This ADF carries the documents stacked in a document stack portion to the document scan portion by one sheet or by some sheets and carries the documents to a document discharge portion after finishing the document scanning in the document scan portion.
In the document scan apparatuses having the ADF, there is a demand for detecting size of the document to be scanned before scanning in the document scan portion.
For example, in the case that a copying machine with flow scanning type document scan apparatuses having ADF carries out an auto magnification selection (AMS) process in which magnifications are selected on the basis of a fixed paper size and variable document sizes and copies an image on the document with enlarging or reducing according to the selected magnification, there is a need to detect the size of the document before the scanning starts.
Various technology has been conventionally provided to detect the document size before the scanning starts.
In most general technology, a document stack portion or a document tray is provided with document size detection means so as to detect the size of documents in the document stack portion.
U.S. Pat. No. 4,739,369 discloses a copying machine having a ADF (document circular feeding apparatus). The ADF carries documents stacked in the document stack portion in order from the lowest layer document and feeds back the document on the highest layer document of documents stacked in the document stack portion after scanning in the document scan portion. In this copying machine, during the first circulation of the document without scanning, the document size is detected by document size detection means provided in a document carrying path. Then, the document is circulated again. During this second circulation, scanning of the document is carried out.
The copying machine, which is provided with the document size detection means in the document stack portion as in the former copying machine, can detect correct document size in case that the size of documents stacked in the document stack portion are unified. However, in case that different size documents are stacked in the document stack portion, namely in the document mixed stack mode, there is a possibility that such copying machine can not detect document size correctly since it only detects the largest size document.
On the other hand, the latter copying machine described in U.S. Pat. No. 4,739,369 can detect size of each document correctly before scanning even in the document mixed stack mode. However, the latter copying machine has low productivity since it circulates the document for detecting the document size and then it circulates the document again for scanning. Further, such document size detection method can be applied only to the document scan apparatuses having the document circular feeding apparatus, hence it lacks generality.